1. Field of the Invention
The present invention relates to transformers equipped with a load tap changer (LTC) and, more specifically, to the use of compensating windings in LTC-equipped transformers to increase or decrease the impedance of the transformer when the LTC changes position.
2. Description of the Related Art
When two transformers are connected in parallel, the impedances of the transformers must match (within 10%) to divide the load approximately equally between the two transformers or to divide the load according to the rating of each transformer. If the transformers to be connected in parallel are equipped with load tap changing windings, then the impedances for each of the tap changer positions must match. If these conditions are not met, then one of the transformers could conceivably carry a continuous overload, resulting in overheating.
Depending upon the insulation practice of the transformer manufacturer and the physical location of the load tap changer winding in relation to the core, the impedance can increase or decrease when the LTC changes position.
To date, no satisfactory solution has been provided to ensure that the impedance of a LTC-equipped transformer is appropriately increased or decreased when the LTC changes position to ensure that a load is properly divided between two parallel transformers.